Level IB: Advanced Fundamentals Seminar Erosion and Sedimentation Processes, Factors and Impacts on the Environment Level IB: Advanced Fundamentals Seminar Education and Training Requirements for Individuals Involved in Land Disturbing Activities Issued May 2009

OVERVIEW Introduction of Erosion and Sedimentation (E&S) Definitions and general stages of E&S Basic processes and factors governing E&S Natural erosion vs. accelerated erosion Impacts of Erosion and Sedimentation (E&S) Environmental impacts Economic impacts Give summary of what will be covered in this 20 minute presentation.

EROSION - The process by which the land surface is worn away by the action of water, wind, ice and gravity Definition of erosion

Predevelopment Construction Erosion is accelerated by human activities when natural vegetation is removed. Construction

Water Erosion Photograph of erosion Water-generated erosion is unquestionably the most damaging type of erosion, especially when dealing with construction sites. Water Erosion

1. Splash Erosion 2. Sheet Erosion 3. Rill Erosion 4. Gully Erosion Types of Water Erosion 1. Splash Erosion 2. Sheet Erosion 3. Rill Erosion 4. Gully Erosion There are four basic types of water erosion, each of which will now be discussed.

Raindrop impact on bare soil Splash Erosion . Erosion by water is a process of breaking loose and transporting soil particles. The energy of raindrops falling on denuded or exposed soils is the key element. The annual impact of raindrops, for instance, has been estimated to average approximately 30 billion foot-pounds or the equivalent of 10 thousand tons of T.N.T. per square mile. Once the soil particle is detached, it is picked up by overland flowing water.

Sheet Erosion As the velocity of overland flowing water increases, additional soil particles are detached and transported causing sheet erosion. Sheet erosion involves the uniform detachment of soil particles by a thin layer of water flowing across the surface referred to as “sheet flow”. Sheet erosion is often somewhat gradual and sometimes can be difficult to detect.

Photograph of rill erosion Rill erosion on the side of a fill slope. RILL EROSION

Photograph of gully erosion Rills that continue to receive concentrated flows can eventually turn into gullies of varying widths and depths. The distinction between a rill and a gully is one of depth. A gully is sufficiently deep that it would not be obliterated by normal tillage operations, whereas a rill is of lesser depth and would be smoothed by use of normal tillage equipment.

TYPES OF WATER EROSION Insert picture here SPLASH SHEET RILL & GULLY This drawing shows all four types of water erosion on a single slope. RILL & GULLY STREAM & CHANNEL

Sedimentation The process by which the eroded material is transported and deposited by Water Wind Ice Gravity It is important to know the difference between erosion and sedimentation. Erosion is the process by which soil particles are detached and sedimentation is the process by which the detached particles are transported and deposited.

SEDIMENT TRANSPORT GA stream following 1/2” of rain June 26, 2001 Unfortunately, this scene is not that uncommon in Georgia after a rain storm. This is a middle Georgia river following just a ½” of rain in the summer of 2001. GA stream following 1/2” of rain June 26, 2001

Photograph of sediment A picture of sediment deposited at a sediment basin discharge point. SEDIMENTATION

Stages in Erosion & Sedimentation 1. Detachment 2. Transport 3. Deposition There are three stages in erosion and sedimentation: detachment, transport, and deposition.

Natural Erosion vs. Accelerated Erosion Natural, or geologic, erosion has been occurring at a relatively slow rate since the earth was formed and is a tremendous factor in creating the earth as we know it today.

Natural (Normal) Erosion Erosion without the interference of man’s activities. The rate is generally small except for stream channel and shore erosion. Natural erosion takes place without the interference of man’s activities and the rate is generally very slow except for stream channel and shore erosion.

Accelerated Erosion Erosion intensified by human activities Example: Farming Example: Construction Erosion can be intensified by human activities when the earth’s surface is exposed. Two major examples include agriculture (farming) and construction.

Estimation of Average Annual Soil Loss Revised Universal Soil Loss Equation (RUSLE) A = R K S L C P A: Average Annual Soil Loss R: Rainfall Erosivity Factor K: Soil Erodibility Factor S: Percent Slope L: Length of Slope C: Cover Management Factor P: Conservation Practice Factor The Universal Soil Loss Equation was first developed in the early 1940s by USDA and has been widely used since the 60s. It is useful to examine the relationship between the different factors impacting erosion rates. The soil loss equation takes into account the following variables: A= is the computed average annual soil loss in tons per acre per year. R is the rainfall factor. The R factor value quantifies the raindrop impact effect. Rainfall energy is directly related to rain intensity. The energy of a rainstorm is a function of the amount of rain and of all the storm’s component intensities. In Georgia R ranges from 250-425 K is the soil erodibility factor. It takes into account that some soils erode more readily than others even when everything else is the same onsite. LS is the topographic factor and takes into account both slope length and slope steepness as both drastically affect the rate of soil erosion by water. C is the cover and management factor or the vegetative over. C is the ratio of soil loss from land with a specified type and amount of coverage. It takes into account whether there is not appreciable vegetative canopy or if there is quite heavy vegetative cover. P is the support practice factor. Unless the land is being used for row crops, P is always equal to 1.00

A = 122.7 tons per acre per year RUSLE Example A = RKLSCP Given: Clarke County (R = 275) Table B-2.1 Cecil sandy loam (K = 0.28) Soil Survey 2:1 slope, 20 feet long (LS = 7.97) Table B-2.2 20% grass cover (C = 0.2) Table B-2.5 No other conservation practices (P = 1.00) Find: Soil loss for the given conditions. Example problem A = 122.7 tons per acre per year *Information taken from the Manual for Erosion and Sediment Control in GA

RUSLE Example A = RKLSCP If you reduce the slope steepness to 3:1 (LS = 4.93) … A = 75.9 tons/acre/year, a 38% reduction in soil loss. or If you increase the vegetative cover to 80% (C = 0.013) … A = 8.0 tons/acre/year, a 94% reduction in soil loss. Example how reducing slope and increasing vegetative cover can have a drastic impact on expected erosion rates.

Expected Erosion Rates (Tons/Acre/Year) 1. Forest Land 1 or greater 2. Farm Land 15 or greater 3. Construction Sites 100 or greater Here is an example of expected erosion rates in Georgia using the Revised Universal Soil Loss Equation. These figures are only general estimates.

Impacts of Construction Activities 1. Removal of organic soil matter 2. Removal of vegetation 3. Reshaping of ground surface contours 4. Exposure of subsoil 5. Changing the pervious ground surface to impervious Construction activities are associated with many adverse impacts that intensify erosion rates.

Factors Affecting Erosion 1. Climatic (rainfall and runoff) Factors 2. Soil Factors 3. Topographic Factors 4. Vegetative Factors The erosion process is influenced primarily by climate, topography, soils, and vegetative cover.

RAINDROP IMPACT & SPLASH EROSION The frequency, intensity, and duration of rainfall influences the volume of runoff in a given area. The erosive potential of raindrop impact is directly related to how intense the particular rain event is.

The potential for soil erosion varies during the year in GA Thunderstorms carry the most intense rainfall. We have more thunderstorms in the summer

Percent Energy The graph of rainstorm energy in Atlanta shows that we can expect the most erosion causing storms in the summer. Particularly in the month of July.

VOLUME AND VELOCITY OF FLOW Photograph of river As the volume and intensity of rainfall increases, the ability of water to detach and transport sediment increases. VOLUME AND VELOCITY OF FLOW

Topography SLOPE GRADIENT SLOPE LENGTH Gradient is expressed as number of horizontal units per unit vertical such as 3 to 1 or 4 to 1 or in percentage as 33 percent or 25 percent. The size, shape and slope characteristics of a watershed influence the amount and duration of runoff. The greater the slope length and gradient, the greater the potential for both runoff and erosion. Velocities of water will increase as the distance from the top of the slope or the grade of the slope increases.

Slope Gradient 4 to 1 or 4:1 means that four feet of horizontal length are required for each foot of vertical change in elevation 1 4 Slope ratios apply to any units of measurement and can be expressed as any equivalent ratio. For example, a 4:1 slope ( 4 feet of run, or horizontal distance, for every 1 foot of rise in elevation) is the same as a 8:2 slope. It can mean 4 inches of run over 1 inch of rise.

Slope Gradient Diagram showing a 4:1 or 25% slope.

Soil Factors Fine sandy & silty soils are more erodible than clay type soils & those with higher percentage of organic matter. The soil type will determine its vulnerability to erosion. Properties determining the erodibility of a soil are texture, structure, organic matter content and permeability. Soil containing high percentages of fine sands and silt are normally the most erodible. Soil types vary across the State of Georgia, and therefore erosive potentials vary from site to site.

Vegetative Factors Absorbs raindrop impact Reduces detachment Roots hold soil in place Slows water flow Adds organic material to the soil Reduces runoff Increases infiltration Vegetative cover is an extremely important factor in reducing erosion from a site.

Picture showing how vegetation protects the soil from raindrop energy.

Photograph of vegetation holding soil in place The roots of vegetation also help hold soil in place preventing sediment detachment. Vegetation holds soil in place

Photograph of vegetation slowing water and trapping sediment Vegetation slows the flow of water, reducing erosion and trapping sediment Vegetation slows the flow of water, allowing for better settlement and trapping of sediment.

Photograph rate and speed of runoff Vegetation allows for infiltration and greatly helps reduce the rate and speed of runoff. Rate and speed of runoff

Photograph Impervious surfaces concentrate rainfall and increase the rate and speed of runoff. This can lead to serious flooding problems.

Vegetation provides organic material Vegetation also provides the soil with organic material which improves the soil’s texture, structure, and permeability.

Impacts of Erosion and Sedimentation 1. Loss of soil productivity 2. Adverse effects on other water resource facilities 3. Loss of reservoir storage capacity 4. Flood impacts 5. Recreational impacts 6. Deterioration of water quality Erosion and sedimentation have many adverse effects on the environment and the economy.

Increased maintenance costs for stormwater management systems E&SC causes increased maintenance costs for stormwater management systems such as flood control structures. As culverts and storage areas fill with sediment, the flood control storage volume decreases.

Decreased Recreational Value E&SC can also have devastating effects on recreation. Nobody wants to swim or fish in a mud hole. Decreased Recreational Value

Screens Out Sunlight = Decline in Plant Growth Biological impacts Suspended sediments, such as clay particles, can block sunlight and result in a decline in plant growth. Aquatic vegetation is very important in aquatic ecosystems in that it produces oxygen and provides food and habitat among many other functions.

Sedimentation Disrupts The Ecosystem Water quality is degraded by increased levels of sediments and nutrients that drain into our State Waters. These conditions can cause prolific weed growth, decreased oxygen levels, changes in species of aquatic plants and animals and even fish kills. Sedimentation Disrupts The Ecosystem

A beautiful North Georgia stream.

Until an irresponsible developer begins land disturbance upstream.

Environmental effects are obvious.

SUMMARY Many processes and factors are involved in erosion and sedimentation Erosion is a natural process, but it can be accelerated by human activities. KEEP BARE SOIL TO AN ABSOLUTE MINIMUM! Impacts of erosion and sedimentation can be devastating to both the environment and the economy Summarize presentation.

Georgia Soil and Water Conservation Commission State Office 706.542.3065 Certification 706.542.1840 www.gaswcc.georgia.gov

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